Even if we supplied a smaller boiler, you would still have the same S20 stoker. The only difference would be less water jacket capacity. by stoker-man

I have seen this comment a few times while efm could have installed the S20 stoker (20 lb of coal an hour max) in efm 350 it really had a S15 stoker installed. (15 lb of coal an hour max). Being an engineer the reality is all units work most efficient when heating requirement match unit size. Over sizing a unit regardless if it is coal, oil or gas bring the efficiencies down. An optimally sized unit for maximum efficiently would run fulltime on the coldest day in the winter. Now we all know that is not practical but running 20 minutes an hour on the coldest day in the winter causes a loss in efficiencies. I have benchmarked tested my 3000 sq feet plus house on the coldest week of the winter and the heat loss was only 55,000 btu an hour.

Last edited by EnergyManager on Thu May 22, 2008 4:41 pm, edited 1 time in total.

Yanche wrote:Combustion efficiency for any fuel is the highest when the correct amount of air, i.e. oxygen is available. In coal appliances there is no provision for adjusting the amount of combustion air except, depending on design, an on/off control. There is a fundamental problem of determining the correct amount of air when the fuel (coal) input is so variable. Current coal appliances have no way to determine this.

In a way, many (if not most) coal appliances DO have a way to adjust air, just not on the fly in a feedback loop like your car. The EFM has the air adjustment with is set according to the coal feed rate to obtain the proper burn rate and performance. My Keystoker has an air control that you use to adjust the air flow to get a full burn at full feed rate.

Now, the EFM has the advantage that when it's not stoking, it's not blowing - it relies on natural draft to keep the fire idling at a very low rate. This air flow is low, so there is not a lot of excess air. My Keystoker, OTOH, blows the same amount of combustion air regardless if it's just holding a tiny idle fire or running flat out. Therefore, at idle, I have a large amount of excess air.

EnergyManager wrote:Even if we supplied a smaller boiler, you would still have the same S20 stoker. The only difference would be less water jacket capacity. by stoker-man

I have seen this comment a few times while efm could have installed the S20 stoker (20 lb of coal an hour max) in efm 350 it really had a S15 stoker installed. (15 lb of coal an hour max). Being an engineer the reality is all units work most efficient when heating requirement match unit size. Over sizing a unit regardless if it is coal, oil or gas bring the efficiencies down. An optimally sized unit for maximum efficiently would run fulltime on the coldest day in the winter. Now we all know that is not practical but running 20 minutes an hour on the coldest day in the winter causes a loss in efficiencies. I have benchmarked tested my 3000 sq feet plus house on the coldest week of the winter and the heat loss was only 55,000 btu an hour.

What's really needed in coal boilers is a clean sheet of paper. A new design. How about a design with dual stokers, one optimized for summer domestic hot water production and second much higher output that kicks in when there's greater heating season demand. And some way to ignite the second stage from the first. Perhaps divert the smaller stage burning gases to ignite the second stage. Perhaps a real small burner that's only a "pilot lite". Perhaps two kinds of coal, rice for the "pilot lite", pea or larger for the bigger stage. I'm sure a little creative thought could come up with a lot of possibilities. Coal will not always be the bargain it is today. Operational efficiencies need to improve.

europachris wrote:The other point to a smaller unit (physically) is many newer homes have finished or partially finished basements with limited room for a large unit. In our home, I have no access to the outside from the mechanical room of our finished basement, therefore I was forced to install a direct vent stove in the finished media room. I would rather have installed a boiler with a hot water coil in the forced air and a plate exchanger for the DHW (or just use the coil). But, that space is quite limited and really something any larger than a KAA-2 Keystoker would not have fit (and also I don't need any more BTU's than that).

But, I love the design and construction of the EFM units. Bulletproof.

Don't mean tfor this to sound the wrong way, but when discussing the size difference between a 350 and a 520 we are talking two fingers difference. It's only a problem if you are two fingers short Scott

I think the coal burning part is at a good efficiency. What i don't understand is why they can't make the boiler part more efficient. Hell, they can get the wood to gasify ,which is sort of like coal, but they use a different capture system to grab the heat. I know my stack temp is way to high to make efficient sense Scott

europachris wrote:The other point to a smaller unit (physically) is many newer homes have finished or partially finished basements with limited room for a large unit. In our home, I have no access to the outside from the mechanical room of our finished basement, therefore I was forced to install a direct vent stove in the finished media room. I would rather have installed a boiler with a hot water coil in the forced air and a plate exchanger for the DHW (or just use the coil). But, that space is quite limited and really something any larger than a KAA-2 Keystoker would not have fit (and also I don't need any more BTU's than that).

But, I love the design and construction of the EFM units. Bulletproof.

Don't mean tfor this to sound the wrong way, but when discussing the size difference between a 350 and a 520 we are talking two fingers difference. It's only a problem if you are two fingers short Scott

If you are Talking about the Square boiler 350 it is 2" less in width and 3 " shorter in heigth Compared to the stardard 520 The 520 Highboys about double that I can't remember the differents in the Round boiler 350 compared to SQ 520 or the Sq 350 but I will find out

stokerscot wrote:I think the coal burning part is at a good efficiency. What i don't understand is why they can't make the boiler part more efficient. Hell, they can get the wood to gasify ,which is sort of like coal, but they use a different capture system to grab the heat. I know my stack temp is way to high to make efficient sense Scott

Well Remember the old ones are tube boiler the New ones are long Flat heat exchangers there has to be a differents Just look in the oldmanual and look at the new one the Numbers are different the 67 manual and the 86 manual Do not match up the older 67 is less BTU's then the New 86 one for the standard 520's

No, just the one in front of the exchanger. And I've recently found out there are pieces thet go into the tubes to create a swirl to cause the flyash to drop in the cleanout? The old guys sure knew their business. Scott

stokerscot wrote:I think the coal burning part is at a good efficiency. What i don't understand is why they can't make the boiler part more efficient. Hell, they can get the wood to gasify ,which is sort of like coal, but they use a different capture system to grab the heat. I know my stack temp is way to high to make efficient sense Scott

A coal boiler can be more efficient. Look at the heat exchanger design of a A-A or AHS boiler, 84-86% operating efficiency. Because of it's design it can extract more heat out of the hot coal gases. Note operating efficiency is different from combustion efficiency.

stokerscot wrote:No, just the one in front of the exchanger. And I've recently found out there are pieces thet go into the tubes to create a swirl to cause the flyash to drop in the cleanout? The old guys sure knew their business. Scott

How Many of them do you want They do nothing for the flyash the where for acting like a heat sinker to help keep the haet in the tubes you have to take them out when cleaning the tubes Every one takes them out and keeps them out it is one of those thing that really does not work like they where design to do More of a PITA then anything but if you want them i know where you can get them

No, I have too many now. I'm not really concerned with a couple percent efficiency. When oil was a buck a gallon(seems like yesterday) I wouldn't have changed my 87% oil boiler out with a higher rated appliance. It just didn't pay. Same with coal. At the prices for these machines it isn't a concern to get a couple percent better efficiency. A couple ton more isn't going to break the bank, yet. Scott

stokerscot wrote:No, I have too many now. I'm not really concerned with a couple percent efficiency. When oil was a buck a gallon(seems like yesterday) I wouldn't have changed my 87% oil boiler out with a higher rated appliance. It just didn't pay. Same with coal. At the prices for these machines it isn't a concern to get a couple percent better efficiency. A couple ton more isn't going to break the bank, yet. Scott

Your efficiency will not go up or down with them they do Nothing but get in the way when cleaning out the tubes and Collect Flyash it was a design that never worked a waste of metal

stokerscot wrote:No, I have too many now. I'm not really concerned with a couple percent efficiency. When oil was a buck a gallon(seems like yesterday) I wouldn't have changed my 87% oil boiler out with a higher rated appliance. It just didn't pay. Same with coal. At the prices for these machines it isn't a concern to get a couple percent better efficiency. A couple ton more isn't going to break the bank, yet. Scott

Your efficiency will not go up or down with them they do Nothing but get in the way when cleaning out the tubes and Collect Flyash it was a design that never worked a waste of metal

I think you might be wrong. The plates serve as a device to keep the intense coal heat from getting sucked out the chimney as fast. All it takes is a simple experiment, check the stack temp without the baffles for a 24 period in the winter and then again with the baffles in place, no other changes. I'll bet the stack is cooler with the baffles in place. No way would EFM continue to put 100 or so extra pounds of expensive steel into the boiler if it wasn't necessary, most customers surely wouldn't complain if they were omitted. As far as removing them for cleaning, how often does it need to be cleaned out, once every year at the most? I'd leave them in as EFM designed.